全文获取类型
收费全文 | 2312篇 |
免费 | 191篇 |
出版年
2023年 | 6篇 |
2022年 | 18篇 |
2021年 | 42篇 |
2020年 | 27篇 |
2019年 | 30篇 |
2018年 | 34篇 |
2017年 | 31篇 |
2016年 | 74篇 |
2015年 | 107篇 |
2014年 | 142篇 |
2013年 | 157篇 |
2012年 | 201篇 |
2011年 | 198篇 |
2010年 | 137篇 |
2009年 | 102篇 |
2008年 | 175篇 |
2007年 | 142篇 |
2006年 | 144篇 |
2005年 | 116篇 |
2004年 | 102篇 |
2003年 | 96篇 |
2002年 | 99篇 |
2001年 | 24篇 |
2000年 | 19篇 |
1999年 | 22篇 |
1998年 | 30篇 |
1997年 | 25篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 14篇 |
1993年 | 11篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 11篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 9篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1973年 | 7篇 |
1968年 | 3篇 |
排序方式: 共有2503条查询结果,搜索用时 15 毫秒
941.
Kristina E. Overkamp Sina Langklotz Marco Aras Stefan Helling Katrin Marcus Julia E. Bandow Kerstin Hoef-Emden Nicole Frankenberg-Dinkel 《Photosynthesis research》2014,122(3):293-304
The cryptophyte phycocyanin Cr-PC577 from Hemiselmis pacifica is a close relative of Cr-PC612 found in Hemiselmis virescens and Hemiselmis tepida. The two biliproteins differ in that Cr-PC577 lacks the major peak at around 612 nm in the absorption spectrum. Cr-PC577 was thus purified and characterized with respect to its bilin chromophore composition. Like other cryptophyte phycobiliproteins, Cr-PC577 is an (αβ)(α′β) heterodimer with phycocyanobilin (PCB) bound to the α-subunits. While one chromophore of the β-subunit is also PCB, mass spectrometry identified an additional chromophore with a mass of 585 Da at position β-Cys-158. This mass can be attributed to either a dihydrobiliverdin (DHBV), mesobiliverdin (MBV), or bilin584 chromophore. The doubly linked bilin at position β-Cys-50 and β-Cys-61 could not be identified unequivocally but shares spectral features with DHBV. We found that Cr-PC577 possesses a novel chromophore composition with at least two different chromophores bound to the β-subunit. Overall, our data contribute to a better understanding of cryptophyte phycobiliproteins and furthermore raise the question on the biosynthetic pathway of cryptophyte chromophores. 相似文献
942.
Richard L. Peters Matthias Speich Christoforos Pappas Ansgar Kahmen Georg von Arx Elisabeth Graf Pannatier Kathy Steppe Kerstin Treydte Ana Stritih Patrick Fonti 《Plant, cell & environment》2019,42(5):1674-1689
Conifers growing at high elevations need to optimize their stomatal conductance (gs) for maximizing photosynthetic yield while minimizing water loss under less favourable thermal conditions. Yet the ability of high‐elevation conifers to adjust their gs sensitivity to environmental drivers remains largely unexplored. We used 4 years of sap flow measurements to elucidate intraspecific and interspecific variability of gs in Larix decidua Mill. and Picea abies (L.) Karst along an elevational gradient and contrasting soil moisture conditions. Site‐ and species‐specific gs response to main environmental drivers were examined, including vapour pressure deficit, air temperature, solar irradiance, and soil water potential. Our results indicate that maximum gs of L. decidua is >2 times higher, shows a more plastic response to temperature, and down‐regulates gs stronger during atmospheric drought compared to P. abies. These differences allow L. decidua to exert more efficient water use, adjust to site‐specific thermal conditions, and reduce water loss during drought episodes. The stronger plasticity of gs sensitivity to temperature and higher conductance of L. decidua compared to P. abies provide new insights into species‐specific water use strategies, which affect species' performance and should be considered when predicting terrestrial water dynamics under future climatic change. 相似文献
943.
Katarina Truvé Peter Dickinson Anqi Xiong Daniel York Kartika Jayashankar Gerli Pielberg Michele Koltookian Eva Murén Hans-Henrik Fuxelius Holger Weishaupt Fredrik J. Swartling G?ran Andersson ?ke Hedhammar Erik Bongcam-Rudloff Karin Forsberg-Nilsson Danika Bannasch Kerstin Lindblad-Toh 《PLoS genetics》2016,12(5)
Gliomas are the most common form of malignant primary brain tumors in humans and second most common in dogs, occurring with similar frequencies in both species. Dogs are valuable spontaneous models of human complex diseases including cancers and may provide insight into disease susceptibility and oncogenesis. Several brachycephalic breeds such as Boxer, Bulldog and Boston Terrier have an elevated risk of developing glioma, but others, including Pug and Pekingese, are not at higher risk. To identify glioma-associated genetic susceptibility factors, an across-breed genome-wide association study (GWAS) was performed on 39 dog glioma cases and 141 controls from 25 dog breeds, identifying a genome-wide significant locus on canine chromosome (CFA) 26 (p = 2.8 x 10−8). Targeted re-sequencing of the 3.4 Mb candidate region was performed, followed by genotyping of the 56 SNVs that best fit the association pattern between the re-sequenced cases and controls. We identified three candidate genes that were highly associated with glioma susceptibility: CAMKK2, P2RX7 and DENR. CAMKK2 showed reduced expression in both canine and human brain tumors, and a non-synonymous variant in P2RX7, previously demonstrated to have a 50% decrease in receptor function, was also associated with disease. Thus, one or more of these genes appear to affect glioma susceptibility. 相似文献
944.
Kento Takahashi Fumika Nakanishi Takeo Tomita Nagisa Akiyama Kerstin Lassak Sonja-Verena Albers Tomohisa Kuzuyama Makoto Nishiyama 《Extremophiles : life under extreme conditions》2016,20(6):843-853
Sulfolobus acidocaldarius, a hyperthermoacidophilic archaeon, possesses two β-decarboxylating dehydrogenase genes, saci_0600 and saci_2375, in its genome, which suggests that it uses these enzymes for three similar reactions in lysine biosynthesis through 2-aminoadipate, leucine biosynthesis, and the tricarboxylic acid cycle. To elucidate their roles, these two genes were expressed in Escherichia coli in the present study and their gene products were characterized. Saci_0600 recognized 3-isopropylmalate as a substrate, but exhibited slight and no activity for homoisocitrate and isocitrate, respectively. Saci_2375 exhibited distinct and similar activities for isocitrate and homoisocitrate, but no detectable activity for 3-isopropylmalate. These results suggest that Saci_0600 is a 3-isopropylmalate dehydrogenase for leucine biosynthesis and Saci_2375 is a dual function enzyme serving as isocitrate-homoisocitrate dehydrogenase. The crystal structure of Saci_0600 was determined as a closed-form complex that binds 3-isopropylmalate and Mg2+, thereby revealing the structural basis for the extreme thermostability and novel-type recognition of the 3-isopropyl moiety of the substrate. 相似文献
945.
The effect of oxygen limitation on xylose fermentation by Pichia stipitis (CBS 6054) was investigated in continuous culture. The maximum specific ethanol productivity (0.20 g of ethanol g dry weight−1 h−1) and ethanol yield (0.48 g/g) was reached at an oxygen transfer rate below 1 mmol/liter per h. In the studied range of oxygenation, the xylose reductase (EC 1.1.1.21) and xylitol dehydrogenase (EC 1.1.1.9) activities were constant as well as the ratio between the NADPH and NADH activities of xylose reductase. No xylitol production was found. The pyruvate decarboxylase (EC 4.1.1.1) activity increased and the malate dehydrogenase (EC 1.1.1.37) activity decreased with decreasing oxygenation. With decreasing oxygenation, the intracellular intermediary metabolites sedoheptulose 7-phosphate, glucose 6-phosphate, fructose 1,6-diphosphate, and malate accumulated slightly while pyruvate decreased. The ratio of the xylose uptake rate under aerobic conditions, in contrast to that under anaerobic assay conditions, increased with increasing oxygenation in the culture. The results are discussed in relation to the energy level in the cell, the redox balance, and the mitochondrial function. 相似文献
946.
Daniela C. Tradowsky Heide Fier Jessica Becker Anne C. Boehmer Ruth Herberz Nadine Fricker Sandra Barth Philipp Wahle Stefanie Nowak Heiko Reutter Rudolf H. Reich Carola Lauster Bert Braumann Thomas Kreusch Alexander Hemprich Bernd Pötzsch Per Hoffmann Franz‐Josef Kramer Michael Knapp Christoph Lange Markus M. Nöthen Kerstin U. Ludwig 《Birth defects research. Part A, Clinical and molecular teratology》2012,94(11):925-933
947.
Bacteria associated with toxic dinoflagellates have been implicated in the production of paralytic shellfish poisoning (PSP) toxins, but it has not been substantiated that bacteria are truly capable of autonomous PSP toxin synthesis or what role bacteria may play in shellfish toxification. In this study, different putatively PSP toxin producing bacteria originally isolated from toxic Alexandrium spp. were exposed to the blue mussel Mytilus edulis. To document that these bacteria accumulated in the digestive tract of the mussels, hybridization techniques that use rRNA targeted oligonuceotides for in situ identification of these bacteria were applied. The mussel hepatopancreas was dissected and paraffin and frozen sections were made. The dissected glands were hybridized with digoxigenin-labelled 16S rRNA oligonucleotide probes. Results demonstrate that mussels will readily uptake and accumulate these bacteria in the hepatopancreas. However, the mussels were not rendered toxic by the ingestion of the bacteria as determined by HPLC with UV detection for PSP toxins and determination of sodium channel blocking activity using the mouse neuroblastoma assay. Thus, although the role that bacteria play in mussel toxification remains unclear, methods are now available which will aid in further investigation of this relatively unexplored area. 相似文献
948.
949.